Is there any way to convert an Eigen::Matrix back to itk::image? - image-processing

Question

I used Eigen library to convert several itk::image images into matrices, and do some dense linear algebra computations on them. Finally, I have the output as a matrix, but I need it in itk::image form. Is there any way to do this?
const unsigned int numberOfPixels = importSize[0] * importSize[1];
float* array1 = inverseU.data();
float* localBuffer = new float[numberOfPixels];
std::memcpy(localBuffer, array1, numberOfPixels);
const bool importImageFilterWillOwnTheBuffer = true;
importFilter->SetImportPointer(localBuffer,numberOfPixels,importImageFilterWillOwnTheBuffer);
importFilter->Update();
inverseU is the Eigen library matrix (float), importSize is the size of this matrix. When I give importFilter->GetOutput(), and write the result to file, the image I get is like this, which is not correct.
This is the matrix inverseU.
https://drive.google.com/file/d/0B3L9EtRhN11QME16SGtfSDJzSWs/view?usp=sharing . It is supposed to give a retinal fundus image in image form, I got the matrix after doing deblurring.

Answer 1

Take a look at the ImportImageFilter of itk. In particular, it may be used to build an itk::Image starting from a C-style array (example).
Someone recently asked how to convert a CImg image to ITK image. My answer might be a starting point...
A way to get the array out of a matrix A from Eigen may be found here :
double* array=A.data();
EDIT : here is a piece of code to turn a matrix of float into a png image saved with ITK. First, the matrix is converted to an itk Image of float. Then, this image is rescaled an cast to a image of unsigned char, using the RescaleIntensityImageFilter as explained here. Finally, the image is saved in png format.
#include <iostream>
#include <itkImage.h>
using namespace itk;
using namespace std;
#include <Eigen/Dense>
using Eigen::MatrixXf;
#include <itkImportImageFilter.h>
#include <itkImageFileWriter.h>
#include "itkRescaleIntensityImageFilter.h"
void eigen_To_ITK (MatrixXf mat)
{
const unsigned int Dimension = 2;
typedef itk::Image<unsigned char, Dimension> UCharImageType;
typedef itk::Image< float, Dimension > FloatImageType;
typedef itk::ImportImageFilter< float, Dimension > ImportFilterType;
ImportFilterType::Pointer importFilter = ImportFilterType::New();
typedef itk::RescaleIntensityImageFilter< FloatImageType, UCharImageType > RescaleFilterType;
RescaleFilterType::Pointer rescaleFilter = RescaleFilterType::New();
typedef itk::ImageFileWriter< UCharImageType > WriterType;
WriterType::Pointer writer = WriterType::New();
FloatImageType::SizeType imsize;
imsize[0] = mat.rows();
imsize[1] = mat.cols();
ImportFilterType::IndexType start;
start.Fill( 0 );
ImportFilterType::RegionType region;
region.SetIndex( start );
region.SetSize( imsize );
importFilter->SetRegion( region );
const itk::SpacePrecisionType origin[ Dimension ] = { 0.0, 0.0 };
importFilter->SetOrigin( origin );
const itk::SpacePrecisionType spacing[ Dimension ] = { 1.0, 1.0 };
importFilter->SetSpacing( spacing );
const unsigned int numberOfPixels = imsize[0] * imsize[1];
const bool importImageFilterWillOwnTheBuffer = true;
float * localBuffer = new float[ numberOfPixels ];
float * it = localBuffer;
memcpy(it, mat.data(), numberOfPixels*sizeof(float));
importFilter->SetImportPointer( localBuffer, numberOfPixels,importImageFilterWillOwnTheBuffer );
rescaleFilter ->SetInput(importFilter->GetOutput());
rescaleFilter->SetOutputMinimum(0);
rescaleFilter->SetOutputMaximum(255);
writer->SetFileName( "output.png" );
writer->SetInput(rescaleFilter->GetOutput() );
writer->Update();
}
int main()
{
const int rows = 42;
const int cols = 90;
MatrixXf mat1(rows, cols);
mat1.topLeftCorner(rows/2, cols/2) = MatrixXf::Zero(rows/2, cols/2);
mat1.topRightCorner(rows/2, cols/2) = MatrixXf::Identity(rows/2, cols/2);
mat1.bottomLeftCorner(rows/2, cols/2) = -MatrixXf::Identity(rows/2, cols/2);
mat1.bottomRightCorner(rows/2, cols/2) = MatrixXf::Zero(rows/2, cols/2);
mat1+=0.1*MatrixXf::Random(rows,cols);
eigen_To_ITK (mat1);
cout<<"running fine"<<endl;
return 0;
}
The program is build using CMake. Here is the CMakeLists.txt :
cmake_minimum_required(VERSION 2.8 FATAL_ERROR)
project(ItkTest)
find_package(ITK REQUIRED)
include(${ITK_USE_FILE})
# to include eigen. This path may need to be changed
include_directories(/usr/local/include/eigen3)
add_executable(MyTest main.cpp)
target_link_libraries(MyTest ${ITK_LIBRARIES})